This invention relates to a system on a locomotive or other railroad vehicle for sensing and continually recording the track curvature on a railroad, particularly in an event recorder so that, upon playback for display of the recorded information, the position of the vehicle may be determined with precision.
It is common practice for locomotives to have event recorders that are analogous to "black boxes" on aircraft. They are used to continuously record on magnetic tape various locomotive conditions, and the railroad engineer's controlling actions. The tape is usually provided in a cassette in the form of a continuous loop and always contains the most recent 12 hours of information.
When desired, the information thus stored is read out and displayed on a continuous sheet of paper. In the case of analog information, it is displayed in the form of an oscillogram with a separate channel for each item of information. The paper is preprinted with scales so that the various analog channels of information can be quantified. Other information also displayed on the continuous sheet of paper may be digital.
A typical event recorder may have two analog channels for speed and traction motor amperage. Other information recorded in digital form includes cumulative distance (e.g. in miles), train air-brake line pressure, throttle position, traction motor amperage, reverser handle position, dynamic brake system activated, and elapsed time. Other systems can have fewer or additional measurements.
In reading out the stored information, a typical event recorder system will print out the speed information as a continuous analog graph with incremental distances indicated by "blips" (momentary deflections of the speed recording pen) as internally calculated by an event record reader as a function of speed and time.
Speed information is derived from the RPM of the locomotive wheels so that indicated speed, which is dependent on exact locomotive wheel diameter, may differ from the true speed. For example, if the wheel diameter is less than a predetermined diameter by one percent for whatever reason, the actual speed will be less, and the distance calculated based on speed will be in error by two miles after traveling 200 miles. The cumulative error in a 12 hour period may thus be as much as five to seven miles. This lack of reliable, precise location information diminishes the value of the event recorder.
The series of curves in a railroad track (the sequence of bends to the left and to the right, and their degrees of curvature and lengths on a segment of railroad) is as unique as a fingerprint, because all track alignment is dependent on terrain. Virtually every American railroad company has documents which describe the characteristics of its branch lines and all segments of main tracks, known as track charts. Track charts describe the principal features of each segment, giving milepost locations, locations of bridges, equipment, towns and sidings, and in particular, for the purpose of this invention, providing a description, curve number, and location of every track curve. Curvatures to the left and right in the direction of travel and the lengths of transition curves from straight track to curvature of the main body of the curve are described, and the degree of curvature of the main body of each curve is specified.
"Degree of curvature" of American railroads is defined as the angle at the center point of the curve which is subtended by a 100-foot chord on the main body of the curve. Mainline tracks generally fall in the range of 0.degree. to 10.degree., with occasional curves up to 15.degree. or so. Yard, spur, and industry tracks can have curvatures as great as 35.degree., and sometimes more.
Track curvature information recorded simultaneously with the other data described above can be used to enhance the usefulness of event recorders installed on railroad locomotives. The curve information generated aboard a moving train could be used in conjunction with incremental distance for the purpose of locating the exact position of an event occurring on the track with an accuracy of less than a quarter, or even a tenth, of a mile.
A track curvature signal can be developed from aboard a locomotive in several ways. The most direct way is to effectively measure the angle of swivel of one or both trucks of the locomotive. A less direct, but equally viable way, is to measure the angle between two rail vehicles, such as the angle in plan view between the locomotive and a rail vehicle next ahead or behind it. However, both ways have a characteristic which, under ordinary conditions, would make the direct (obvious) transducer arrangement for generating a curvature signal unacceptably inaccurate. The locomotive trucks (the wheel assembly and frame) have a feature called "lateral motion" which permits the body of the locomotive, and of other rail vehicles, to move laterally relative to the track centerline (and therefore to the trucks) in order to soften the ride in that direction.
The coupler and draft gears on railroad locomotives and other rail vehicles are arranged to permit some relative longitudinal movement between any two vehicles (they become closer together or farther apart), also partly for the purpose of softening the riding qualities--this time in the longitudinal direction. Once again, this feature makes the direct (obvious) transducer arrangements unacceptably inaccurate and/or cumbersome. One of the objectives of this invention is to provide a transducer arrangement for generating a curvature signal on board a vehicle which overcomes the shortcomings that normally would occur when lateral displacement of the rail vehicle trucks or longitudinal displacement between rail vehicles occurs.